The present invention relates to a facsimile apparatus capable of shortening a period of time necessary for setting up a transmission modem rate and, thereby, a period of time over which it occupies a transmission line.
Generally, a facsimile apparatus is operated in conformity to a transmission control procedure (Recommendation T.30) standardized by CCITT (Consultative Committee of International Telegraph and Telephone). The transmission control procedure is roughly made up of five sequential phases: phase A for setting up a call, phase B for confirming functions and others of a terminal before transmitting video data, phase C for transmitting video data, phase D for confirming continuation of the transmission condition after the transmission of video data, and phase E for disconnection.
In the phase B mentioned above, a modem rate for the transmission of video data is also set up. Specifically, an apparatus at a calling station performs modem training with an apparatus at a called station, starting with the maximum modem rate (e.g. 9600 bits per second). When the calling apparatus has failed to train the called apparatus at the maximum modem rate, it repeats modem training while sequentially shifting down the modem rate, thereby determining a usable modem rate. Such modem rate set-up is dependent upon the condition of the line interconnecting the calling and called stations and, usually, a relatively high modem rate is set up if the line is well conditioned. A transmission control procedure signal per ce is transmitted at a rate as low as 300 bits per second which insures transmission with no regard to the line condition.
Meanwhile, in the case where a calling station knows an upper limit of modem rates assigned to a remote station, which it intends to call, through the past communications with the latter and/or a line condition is approximately presumable from the traffic in a particular time zone chosen for transmission, the calling station to some extent can select an adequate modem rate relying on such known and presumable information. In addition, where the call is meant particularly for an overseas station, it is possible to determine to a certain degree an adequate modem rate taking the season into account since the line condition in some measure is dependent upon the season.
As described above, considering a particular remote station and the dates or times of past communications therewith will enable a calling station to select a usable modem rate to a certain degree. Nevertheless, since the prior art apparatus starts modem training at the maximum modem rate as previously discussed, it inevitably consumes an extra time in setting up a modem rate. Such is reflected by an increase in the period of time for which the calling station occupies the line and, therefore, in transmission cost.